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研究生： 徐麗婷
Hsu, Li-Ting
論文名稱： 明亮類星體與屏蔽類星體之間的演化關係
The evolutionary connection between unobscured and obscured quasars
指導教授： 陳林文
Chen, Lin-Wen
學位類別： 碩士
Master
系所名稱： 地球科學系
Department of Earth Sciences
論文出版年： 2011
畢業學年度： 99
語文別： 英文
論文頁數： 54
中文關鍵詞： 活躍星系核 、屏蔽類星體 、類星體
英文關鍵詞： AGN, dusty quasar, QSO
論文種類： 學術論文
相關次數： 點閱：929  下載：5 
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    • 受塵埃屏蔽的二型類星體在本質上與一型類星體一樣明亮，但大量塵埃的遮蔽使得這類天體看起來十分昏暗黯淡。一型與二型類星體之間的關係目前還不是很明確。不論二型類星體中的塵埃是分佈在鄰近核心的周圍或是在核心的塵埃環上，它們的來源與分佈的空間尺度對於了解二型類星體來說都十分重要。在本論文中，我們藉由統計分析類星體的多波段性質，包括環境、塵埃性質、電波光度及愛丁頓比值，來研究一型與二型類星體間的演化關係。我們發現在二型類星體周遭半徑 1.5 Mpc 範圍內的星系數目比一型類星體多出1.4倍，這意謂著這兩種類型類星體的來源可能並不相同。再者，在二型類星體中的塵埃含量與核心產生的能量有關係：塵埃含量愈大，其中心的電波光度愈強，吸積率則愈小；然而，在一型類星體中，塵埃含量與這兩個性質卻沒有什麼關連性。這樣的差異可能並不單由對核心塵埃環以不同視線方向的觀察所造成，也可能歸因於更大尺度分佈的塵埃影響。最後，經由塵埃量與愛丁頓比值隨著宇宙時間的演化趨勢，我們發現，二型類星體的塵埃量愈來愈少，而吸積率則愈來愈高，最終可能演化成塵埃少且明亮的一型類星體。因此我們的研究認為，二型類星體應該是處於類星體的早期演化階段。

    Type 2 quasars (QSO2) are intrinsically as luminous as type 1 quasars (QSO1), but obscured by a large amount of dust. Furthermore, the evolutionary connection between QSO1 and QSO2, if any, remains unclear. One key clue to understand the nature of type 2 quasars is to investigate the scale and origin of the dust that causes obscuration, whether it is attributed to circumnuclear dust or to a dust torus in the galactic nucleus. In this thesis,we study the evolutionary connection between QSO1 and QSO2 by statistical analyses of several multiwavelength properties including the environment,dust property, radio luminosity, and Eddington ratio. We find that the average galaxy counts surrounding QSO2 within R = 1.5 Mpc are greater than those of QSO1 by a factor of  1.4, implying that these two types of quasars have different origins. In addition, the dust amount in QSO2 is related to the central power; the more dusty QSO2 prefer to have higher radio luminosities and lower accretion rates, whereas QSO1 have a weak correlation between dust amount and central power. This different dust-radio luminosity relation between QSO1 and QSO2 implies that the dust extinction is not only due to the orientation effect of torus, but also attributed to a larger-scale dust. Finally, based on the evolutions of dust amount and Eddington ratio, we demonstrate that the amount of dust in QSO2 diminishes while their accretion rates increase with time, involving that QSO2 may turn into clear and bright QSO1. Our study suggests that QSO2 are at an early evolutionary stage of QSO1.

    1. Introduction.................................1 1.1 Unfied model of AGN.........................1 1.2 The nature of type 2 quasars................1 1.3 Physical properties of QSO2 ................5 1.3.1 Environment...............................5 1.3.2 Radio properties .........................5 1.3.3 Eddington ratio ..........................5 1.3.4 Summaries for the chapters................6 2. Multiwavelength Data.........................7 2.1 Quasar samples from SDSS....................7 2.1.1 Optical-selected Type 2 quasars ..........7 2.1.2 Optical-selected Type 1 quasars...........8 2.2 Radio counterparts from FIRST ..............9 2.3 Near-Infrared counterparts from 2MASS.......9 3. Data Analyses...............................11 3.1 Environment of quasars.....................11 3.1.1 Galaxy selection criterion...............11 3.1.2 Results..................................13 3.2 Radio properties...........................18 3.2.1 1.4 GHz radio luminosity.................18 3.2.2 Radio loudness...........................18 3.3 Dust property..............................25 3.3.1 Relative color of QSO1...................28 3.3.2 Relative color of QSO2...................29 3.3.3 Results .................................32 3.4 Eddington Ratio............................35 3.4.1 Estimate of SMBH mass and Eddington ratio.....35 3.4.2 Correation between Eddington ratio and other physical properties.....................................35 3.5 Neutral hydrogen column density............43 3.6 ULIRG-like QSO2............................46 4. Discussion..................................47 4.1 Relation between L1:4 GHz, radio loudness and dust...47 4.2 Environment vs. radio loudness.............48 4.3 Correlation between Eddington ratio and other properties ...............................................48 4.4 Evolutionary connection between QSO1 and QSO2...49 5. Conclusions.................................51 6. References..................................53

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